Enhanced modeling of vehicle-induced turbulence and pollutant dispersion in urban street canyon: Large-eddy simulation via dynamic overset mesh approach

This study presented a novel application of large-eddy simulation (LES) with a dynamic overset mesh approach to simulate vehicle-induced turbulence in a two-dimensional street canyon. The simulation incorporated moving vehicle entities to emulate two-way traffic, with each vehicle equipped with a pollutant source to simulate pollutant dispersion. Comprehensive long-term statistical analyses were conducted to compare the simulated turbulence with those produced by the conventional approach (where vehicle-induced momentum was not considered) and the quasi-steady method (where vehicle motion was simplified as momentum sources). The results revealed that the presence of moving vehicle entities significantly distorted the primary circulation within the canyon, altering the transport pathways of both lateral momentum and air pollutants. The motion of vehicle entities also induced a substantial amount of turbulence, resulting in different pollutant removal mechanisms at the top of the canyon. The ensemble-average analysis revealed a downwash followed by an upwash within a cycle of vehicle movement, which largely contributed to momentum and pollutant transport. These findings underscored the need for considering the moving entities in LES approaches to enhance vehicle-induced turbulence modeling. Other factors influencing the simulation were discussed, aiming to guide more accurate and reliable turbulence modeling in urban environments.